Predicting Coalescence of Particle Encrusted Drops by Interfacial Shear Rheology

Food, pharmaceutical and cosmetic formulations are quite often Pickering type emulsions in which the interfaces of at least two immiscible liquids are stabilized by excipient particles which have crystallized out from one of the liquid phases. We demonstrate that the resistance provided by interfacial particle networks to coalescence can be predicted from coalescence depends the surface concentration of the particles laden dispersed droplets. The surface coverage concentration is uniquely determined by the emulsion making process. We treat this network as an elastic solid layer and interpret the onset of coalescence as to occur when the surface layer undergoes yielding under extension, we estimate the force on a droplet required to induce coalescence. Further, we extend this analysis to emulsions exposed to varying levels of centrifugal force and predict the amount of the dispersed phase recovered. We verify our model predictions by centrifuging the emulsions with different surface coverage and measuring the separated dispersed phases.